21st January 2012 04:10 PM
A 455kHz IF transformer is narrow-band for communications.
A 10.7MHz IF transformer is wideband for low distortion and wide frequency response for FM stereo receivers.
21st January 2012 09:21 PM
Sorry, complete nonsense - dual conversion is for communication receivers, the reason for it is to give low bandwidth voice quality only.
Originally Posted by transistor495
A 455KHz IF is FAR too low to give decent bandwidth or HiFi quality.
AG seems to have his own warped opinion about anything that isn't full HiFi quality, and while communication receivers can give excellent voice quality (which is their reason for being) HiFi it isn't, and doesn't want to be.
Coincidently, there's no 'magic' reason for 10.7MHz IF - it's simple a compromise giving reasonable selectivity, reasonable bandwidth, at a reasonable cost and ease of manufacture.
With modern filters (rather than pre-WWII transformers) you can make receivers that greatly exceed the performance of 10.7MHz IF receivers, in every aspect. Many more modern communication receivers get their greatly improved performances from far higher IF frequencies.
21st January 2012 09:52 PM
I was never an amateur radio HAM.
In North America local telephone calls are free for any duration and sound better or the same as narrow band radio so I never used radio communications except for cell phones and FRS walkie-talkies.
29th January 2012 03:34 PM
Well, not that easy
I was having a hard time getting this one working though, I had some results with severe overloading and lots of stability problems.
Within a 5 meter circle, I can move around to get a somewhat clear reception, I had noticed this with other portables also, but in my case its much severe, I've attached front-end RF amp though.
But all I can say now is I got the basic superheterodyne principle working for FM demodulation, but need more experiments to prove a nice working receiver. Also I'm running bit out of time.
So signing-off temporarily from this now and will update this thread after some time.
1st May 2012 04:56 PM
Last edited by Ramos; 1st May 2012 at 04:56 PM.
30th May 2012 05:33 PM
Well, never noticed this reply ;-)
Originally Posted by Ramos
Those articles indeed looks interesting, but mine was to prove it with an easiest/simplest circuitry -perhaps I may need to conduct few more crude experiments and study. I'm ready to re-open the strategy -well..the curiosity never ends, sometimes the results will be horrible though
30th May 2012 09:45 PM
A breadboard is usually not used for radio circuits because its stray capacitance between the many rows of contacts and between all the wires is far too much. The many long wires cause interference within the circuit and they pickup all kinds of external interference.
For many years, 10.7MHz crystal filters have been used in the IF of an FM radio instead of 10.7MHz transformers.
7th June 2012 02:56 AM
I was getting into the track by doing a simple AM Superhet by using a single BF494 mixer+converter and a YS414 IF amp+detector. It works fine. This can be one of the simplest Superheterodyne designs. It has built in AGC provided by the chip. Audio is clean but it lacks the full punch which I assume because of YS414 has only output for a crystal earphone. I may need pre-amplification of the audio before sending to the power amp. But the current setup is still acceptable though.
Very quick experiment. Thanks for looking, cheers
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